Checking Fourth Gear Switch

Disconnect plug from ignition switch-over valve and connect voltmeter. Operate vehicle on dynamometer or road. When transmission switches from third to fourth gear, ignition retard should be cancelled and voltmeter should read 13 volts. When shifting from fourth to third gear when coasting, ignition should be retarded at engine speeds below 3200 RPM and voltmeter reading should return to zero. If no ignition switch-over occurs, disconnect wire from transmission switch and connect to ground. Start engine and check ignition timing. If ignition timing is now cancelled, replace transmission oil pressure switch. If ignition retard is not cancelled, replace 12 prong relay box.